1. Field of the Invention
The present invention relates to a shield type magnetoresistance effect head.
2. Description of the Related Art
In recent years, magnetic recording is made at a high density, and a high recording density system, e.g., an HDD having 1 Gb/inch.sup.2, has become commercially practical. And a higher recording density is being demanded increasingly. As a reproducing head for such a high recording density system, attention is being given to a magnetoresistance effect head (hereinafter called "MR head") making use of a magnetoresistance effect in which an electrical resistance of a magnetic film, a magnetic multilayered film or the like is varied by an external magnetic field from the viewpoint of improvement of a reproducing sensitivity.
FIG. 6 shows the configuration of a typical shield type MR head. In the drawing, reference numeral 1 denotes a substrate made of Al.sub.2 O.sub.3. TiC or the like. On the substrate 1 is formed a lower magnetic shielding layer 3 which is a crystalline soft magnetic film of sendust, permalloy or the like or an amorphous soft magnetic film of CoZrNb alloy or the like with an insulating layer 2 made of Al.sub.2 O.sub.3 or the like intervened between them.
A magnetoresistance effect film (MR film) 5 is formed on the lower magnetic shielding layer 3 with an insulating film 4, which forms a lower reproducing magnetic gap, formed between them, and a pair of leads 6 are formed on both ends of the MR film 5 to form a magnetoresistance effect element (MR element) 7. On the MR element 7 is formed an upper magnetic shielding layer 9 which is made of a soft magnetic film similar to the lower magnetic shielding layer 3 with an insulating film 8, which forms an upper reproducing magnetic gap, formed between them.
To detect a signal magnetic field of such a shield type MR head, for example, a sense current is flown through the pair of leads 6, and the MR film 5 is measured for its change in electrical resistance involved with a change in average magnetization direction.
Meanwhile, the MR film is proceeding toward practical utilization provided with a giant magnetoresistance effect (hereinafter called "GMR") having a magnetoresistance change ratio (MR change ratio) of more than 3%. Especially, attention is directed to a spin-valve type GMR film which has a sandwich film with a ferromagnetic film/nonmagnetic film/ferromagnetic film structure. The spin-valve type GMR film obtains GMR by stacking one of the ferromagnetic films on an antiferromagnetic film or the like to make exchange coupling, pinning magnetization of the ferromagnetic film, and changing the magnetization direction of the other ferromagnetic film by an external magnetic field (signal magnetic field).
The GMR film described above, however, has a drawback that its properties are easily deteriorated due to the surface roughness of an under layer because the respective films have a thin thickness of about a few nm. Especially, where a crystalline soft magnetic film of sendust, permalloy or the like, which is mainly used for the existing MR head, is used as the magnetic shielding layer, there is a disadvantage that since the surface roughness is easily caused with the growth of crystal particles, the properties of the GMR film are easily deteriorated due to the surface roughness of the magnetic shielding layer.
Specifically, a so-called magnetization-free layer of the spin-valve type GMR film needs soft magnetic characteristics, but a coercive force H.sub.c of the GMR film in a direction of the axis of hard magnetization becomes high due to the surface roughness of the under layer, deteriorating the soft magnetic characteristics. The deterioration in soft magnetic characteristics of the GMR film causes Barkhausen noise.
The roughness of the under layer described above is reflected in the surface roughness of the respective component films of the GMR film and increases their roughness. Thus, magnetostatic coupling is enhanced by a shape effect of the interfacial roughness in the GMR film, and an interlayer coupling field H.sub.in is increased. The increase of the interlayer coupling field H.sub.in leads in a disadvantage that the MR head does not operate stably.
As described above, the MR film of a spin-valve type is highly expected in obtaining a high MR change ratio structurally, but where the crystalline soft magnetic film of sendust, permalloy or the like which is mainly used for the existing MR head is used as the magnetic shielding layer, it is hard to decrease the surface roughness. Consequently, there are drawbacks that the GMR film is deteriorated in view of soft magnetic characteristics, and its interlayer coupling field is increased, resulting in degrading its performance as the GMR head.
Accordingly, a GMR head having a crystalline soft magnetic film as the magnetic shielding layer is demanded that good properties can be obtained with good reproducibility by making it possible to suppress the soft magnetism of the GMR film from being deteriorated and the interlayer coupling field from being increased even when the GMR film has a large surface roughness on its under layer.